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On Aug. 4, 1972, U.S. military pilots flying south of Haiphong harbor in North Vietnam saw something unexpected. More than two dozen sea mines suddenly鈥攁nd without apparent explanation鈥攅xploding in the water.听

Now, CU Boulder engineering professor Delores Knipp and her colleagues have dug into this four-decades-old naval mystery. In a commentary , the team reports that the mines were likely triggered by magnetized gas flung at Earth from a recent solar storm.听

The research, which Knipp said was inspired by 鈥渁 fragment of a memory,鈥� uncovers a chain of events around the sun and on Earth that had largely been lost to history. It also suggests that the 1972 solar storm was more serious than many researchers at the time suspected.听

Knipp, a research professor in the Ann and H.J. Smead Aerospace Engineering Sciences Department (AES), said that the case of the exploding mines highlights the world鈥檚 current vulnerability to a similar space weather event.

鈥淚n the process of researching this event, I realized that this was, in fact, a great storm. But it was also such an odd storm in the way it developed and the way it hit the earth,鈥� said Knipp, also of the Colorado Center for Astrodynamics Research (CCAR). 鈥淲hat this event does is give us a sense of range of what these great storms could look like.鈥�

Unexpected visitors

Knipp, a 22-year veteran of the U.S. Air Force, said that she has always had a 鈥�passion for rooting around in dark, dusty archives.鈥� Her interest in the 1972 storm began with a chance conversation with a colleague, who at the time was working as a postdoctoral fellow at the precursor to the National Oceanic and Atmospheric Administration鈥檚 .听

鈥淗e remembered there being a group of navy men in uniform and a couple of folks in dark suits who were visiting his boss,鈥� Knipp said.听

Her colleague didn鈥檛 know what transpired in that meeting, but he knew it had something to do with the military implications of a recent solar storm.听

With a bit of digging, Knipp found a naval report that opened up the floodgates. The report, declassified sometime around 1990, discussed the spontaneous detonations of dozens, and maybe more, sea mines in Asia. Those mines had been part of a Vietnam War campaign called 鈥淥peration Pocket Money.鈥�

To her surprise, the report linked those detonations to solar activity.听

鈥淚 started reading this report, and I said, 鈥榃ow, this really happened,鈥欌�� Knipp said.

She and her colleagues wanted to know more. They tracked down a series of reports from scientists in the U.S., Japan and Europe that, Knipp said, had been filed away and mostly forgotten.

According to those documents, ground-based observatories recorded four solar flares, or ejections of energy from the sun, between Aug. 2-4. The third one was gigantic, and likely produced an event called a coronal mass ejection.

鈥淭hat鈥檚 when we knew that something wicked this way comes,鈥� Knipp said.

Carrington-class event

But no one realized just how soon: The magnetized clouds of gas ejected by such events usually take about three days to reach Earth. This time, it took only 15 hours.听

When the solar material hit, it pummeled Earth鈥檚 magnetosphere, the sheath formed by the planet鈥檚 magnetic field that guards against outside radiation. The resulting interaction caused major fluctuations in power grids in Canada and the northern United States.听

It also set off the sea mines, which were designed to register the magnetic fields created by passing ships. 听

Altogether, Knipp believes that the 1972 solar storm was on par with the famed Carrington Event, a significant space weather event that astronomers recorded in 1859. Still, many solar observers at the time chalked听the 1972 solar storm up to a routine occurrence.

鈥淚 think people forgot about it,鈥� Knipp said. 鈥淭hey didn鈥檛 know about the sea mine problem and the effect on the power grids got published in engineering journals, not science journals.鈥澨�

Knipp added that the solar storm, and the subsequent explosion of dozens of sea mines, should be seen as a cautionary tale. People today are far more dependent on space satellites for communications and navigation than they were in 1972鈥攁nd those satellites sit right in the path of potential solar storms.听

CU Boulder undertakes a wide range of research around predicting and safeguarding against space weather events, including at its newly-launched Space Weather Technology, Research and Education Center.听

Co-authors on the new study include Brian Fraser of the University of Newcastle in Australia and Margaret Shea and Don Smart, both retired from the Air Force Research Laboratory. Knipp is also a senior research associate at the High Altitude Observatory of the National Center for Atmospheric Research.